The present disclosure relates to an image reading device that reads a document and generates image data, and to an image forming apparatus including the image reading device.
It may be performed to irradiate both sides of a paper sheet with light for detection about the paper sheet. For example, a following image forming apparatus is known. Specifically, there is known an image forming apparatus, which includes a printer engine that performs image formation, supplies a medium (paper sheet) to the printer engine, irradiates the medium with light at a predetermined position in a conveyance path, receives transmitted light through the medium, receives reflected light from the medium, determines a thickness of the medium based on received light detection signals of the irradiation light, the transmitted light, and the reflected light, and performs predetermined control based on a result of the determination. In this known image forming apparatus, printing is performed according to a thickness of the paper sheet based on a result of detection of the thickness of the paper sheet. For example, transfer current or temperature of a fixing device is changed according to the thickness of the paper sheet.
The image reading device (scanner) is provided with a light source. The light source emits light to a document. The document reflects the light. The reflected light enters an image sensor. The document is read based on the light reflected by the document.
When reading a document, there may be a need to obtain information about the document. For example, there may be a need to obtain information such as an end position of the document, inclination of the document, and presence or absence of a hole in the document. Recognition of end positions enables to detect an accurate size of the document. Accurate detection of inclination of the document enables to accurately correct the inclination. Accurate detection of presence or absence of a hole in the document enables to easily delete an unnecessary part of the image data corresponding to the hole.
In order to obtain information about the document, it is necessary to distinguish a part with document data from a part without document data in the image data obtained by reading. In other words, it is necessary to distinguish a pixel having read document data from a pixel having no read document data in the image data.
Conventionally, a white color member is used as a background member of a document. In other words, a white color plate is disposed on the backside of the document viewed from the light source and the image sensor. A density value (pixel value) of a pixel having no read document data becomes a white (bright) value. Further, the paper sheet usually has white color. There is a problem that in the image data read with the reflected light, a pixel having read document data cannot be correctly distinguished from a pixel having no read document data.
The known image forming apparatus described above irradiates the paper sheet with light in the same manner as the image reading device. On the basis of the determined reflectance and transmittance, it is determined whether the paper sheet is thick paper or not. However, it is not possible to distinguish a pixel having read document data from a pixel having no read document data in the image data. Therefore, the above-mentioned problem cannot be solved.